Bearings are devices that permit constrained relative motion between two parts. A rolling element bearing, sometimes referred to as a rolling bearing, is a bearing which carries a load by placing rolling elements, such as rollers or balls, between two bearing rings. The rolling elements are typically lubricated with grease. A particularly common type of rolling element bearing is a ball bearing. A ball bearing has inner and outer rings between which balls roll. The rings typically feature a groove (also known as a race or raceway) which is usually shaped so that the balls fit slightly loosely in the grooved ring.
Bearing closures serve to exclude contamination, contain lubricants and protect the bearing from internal damage whilst being handled. Bearing closures are available in two basic types: contact bearing closures (often referred to as “seals”) and non-contact bearing closures (often referred to as “shields”). Bearing closures are typically attached to the outer ring of a bearing. Contact bearing closures typically contact both the inner and outer rings. While such an arrangement is effective at reducing contamination and lubricant loss, the contact of the bearing closure with both rings increases the torque and reduces the maximum speed capability of the bearing. In contrast, non-contact bearing closures do not contact the inner ring. There is therefore a gap between the non-contact bearing closures and the inner ring. While such an arrangement leads to reduced torque, the protection against contamination and lubricant loss may be reduced. Lubricant and/or contaminants may leak through the gaps between the non-contact bearing closure and the inner ring by surface wetting. This leakage is enhanced by a dynamic pumping effect of the bearing. While the dynamic pumping effect can be reduced by reducing the size of the gap, this may enhance leakage via the capillary effect. In addition, reducing the size of the gap is limited by the need to avoid contact between the non-contact bearing closure and the inner ring. Accordingly, there is a need for a bearing closure which exhibits low levels of torque together with high protection against contamination and lubricant loss.
The present invention seeks to tackle at least some of the problems associated with the prior art or at least to provide a commercially acceptable alternative solution thereto.